a) Field of the Invention
The present invention relates to an electronic-laser system, and more particularly to an electronic-laser system for outputting a radio-frequency signal and a pulse laser beam synchronous with the radio-frequency signal.
b) Description of the Related Art
An acoustic-optic mode locked laser oscillator is known which outputs a laser beam locked in the phase of a master radio-frequency signal.
The acoustic-optic mode locked laser oscillator has an acoustic-optic device in an optical path of an optic resonator. Upon application of a radio-frequency signal, the acoustic-optic device generates a standing wave in a laser beam transmission medium to Bragg-reflect a laser beam. The amount of Bragg reflection changes with a displacement amount of each position in the transmission medium, and the transmission loss of the optic resonator changes synchronously with the applied radio-frequency signal.
Laser oscillation occurs only when an amplification amount of a laser beam in a stimulated emission part and a loss amount of the laser beam in the acoustic-optic device satisfy particular conditions. When the conditions are satisfied, a pulse laser beam is output synchronously with the radio-frequency signal applied to the acoustic-optic device.
A pulse electron beam is obtained by applying a pulse laser beam to a photocathode and accelerating emitted photoelectrons in an acceleration cavity. In this case, it is necessary to synchronize a radio-frequency electric field induced in the acceleration cavity with a pulse laser beam applied to the photocathode. By using the acoustic-optic mode locked laser oscillator, a pulse laser beam can be locked in a radio-frequency signal.
An upper frequency limit of a radio-frequency signal applied to the acoustic-optic device of an acoustic-optic mode locked laser oscillator is about 500 MHz. In contrast with this, the frequency of a signal applied to the acceleration cavity to accelerate photoelectrons emitted from a photocathode is about several GHz. This signal is therefore obtained from a radio-frequency signal applied to the acoustic-optic device, by multiplying it with a frequency converter. The multiplied signal is applied to the acceleration cavity. The multiplied signal is power-amplified before it is applied to the acceleration cavity. While this radio-frequency signal is multiplied by the frequency converter and amplified by an amplifier, a phase of the radio-frequency signal shifts. As the pulse width of a pulse electron beam becomes narrow, this phase shift poses some problem.